Variable transmittance optical filter with substantially co-planar electrode system

A method of preparing a variable transmittance optical filter comprising the steps of:

• (a) providing a first layer comprising a first substantially transparent substrate, and:
• (i) etching into a layer of substantially transparent electrically conductive material disposed thereon a substantially co-planar (SC) electrode system pattern, the SC electrode system pattern comprising at least one pair of electrically separate electrodes arranged in a substantially co-planar manner, each pair of electrically separate electrodes comprising a first electrode and a second electrode;
• or
• (ii) printing onto the first substrate a substantially co-planar (SC) electrode system pattern using a conductive ink, the SC electrode system pattern comprising at least one pair of electrically separate electrodes arranged in a substantially co-planar manner, each pair of electrically separate electrodes comprising a first electrode and a second electrode;
• (b) disposing a second layer proximate to the SC electrode system pattern, the second layer comprising a transition material comprising a compound that is both photochromic and electrochromic that is capable of dynamically varying the degree of visible light transmittance on application of an electric voltage;
• and
• (c) providing an electrical connection system electrically connecting the SC electrode system pattern to a source of the electric voltage;
• wherein the first electrode and the second electrode of each pair comprise primary finger-like structures and the primary finger-like structures of the first electrode are interdigitated with the primary finger-like structures of the second electrode.